Neutron ray generators have been developed for a variety of uses. Most conventional neutron generator systems are employed in the technique of neutron activation analysis in which high speed (fast) neutrons generated by directing an ion beam in an accelerator tube are directed at a suitable target which then emits high energy neutrons. The composition of the test material irradiated with high energy neutrons is determined by analyzing the emissions from the test material.
In other applications, such as neutron radiography high energy (fast) neutrons are not suitable, and such fast neutrons must be reduced to low energy (thermal) neutrons by discharging a high energy neutron beam into a suitable moderator medium.
A neutron radiography inspection device employing an ion accelerator system is disclosed in the copending application Ser. No. 483,847 of William E. Dance, filed April 13, 1983, entitled THERMAL NEUTRON COLLIMATOR. The inspection device includes a housing containing a moderator material with a high energy neutron source positioned therein. A collimator mounted in the housing discharges a beam of thermal neutrons issuing from the moderator material as the result of bombardment of hydrogen protons in the moderator material with high energy neutrons emitted from an ion accelerator tube.
Although ion accelerator neutron radiography row systems compare favorably with radiography systems using neutron emitting isotopes, radiographs produced by ion accelerator systems had not prior to systems of the type described in invention disclosures by W.E. Dance been of the same quality and resolution as in systems using neutron emitting isotopes. However, ion accelerator systems have significant advantages over the isotope systems. They are less costly, have on/off capability and are useful in portable neutron radiography applications, where the weight of the shielding required for large isotope systems is prohibitive in a portable system. Thus, in portable systems, ion accelerator systems are preferred.
Since the radiograph exposure time is inversely related to the magnitude of the thermal neutron flux, inspection operations with portable neutron radiography systems using ion accelerator systems could become much more efficient if the thermal neutron flux of these systems could be increased.